The rankings are based on how well people predicted individual states, with the penalty for missing a state being the percentage margin of victory. This penalizes people less for getting close states wrong, and more for losing big. The values of the various states, via Huffington Post, are MN=7.7 WI=6.7 NV=6.6NH=5.8 IA=5.6PA=5.2 CO=4.7 VA=3.0 OH=1.9 FL=0.9.

I use accuracy of popular vote prediction to break ties. I'm working with a popular vote margin of 3.9%. Since many people didn't try to predict the popular vote, this is somewhat artificial. So I've added the letter-grade component on the right, which doesn't take popular vote into account, except in the case of the Daily Kos folks who get an A+ for getting the popular vote closest to right.

For now, I'll outsource commentary on the success of Nate and the other poll aggregators to xkcd:

There are a couple other statistical analyses of election prediction accuracy up at the Center for Applied Rationality and Margin of Error. They include predictions from DeSart & Holbrook, Margin of Error, and InTrade, which aren't in your table.